In general, a pillow serves to support the head of a user such that the user can remain in a comfortable position while sleeping, and thus generally has a predetermined height and a suitable cushioning function. Such a pillow includes a pillow body filled with a stuffing and a pillow cover covering the pillow body. The stuffing may be implemented as buckwheat chaff, rice chaff, latex, sponge, cotton, hair, a functional material, or the like.
People sleep in a variety of postures, i.e. people lie on backs, sides, or stomachs. When a person rests with the head supported on a pillow while lying on his or her back, the back of the head, the cervical spine, and the back are substantially in line, such that the user may not be significantly uncomfortable even if the height of the pillow used is relatively low. However, when the person attempts to sleep on the side with the pillow of the same height, the cervical spine becomes curved due to the difference in the height between one shoulder and one side of the face, causing the person to be uncomfortable. In contrast, when a relatively higher pillow is used, the person may feel relatively comfortable when lying on the side. However, when the person lies on his or her back, the head may be raised, whereby discomfort is likely.